With this update of her popular 1960 Elegant But Easy Cookbook, Burros adds her contribution to a lengthening list of revised cookbook classics. Faithful readers will recall that the original featured make-ahead party fare; the same is true in the new edition. Here, however, the hors d'oeuvres, the fish, meat and vegetarian entrees, as well as side dish, salad and dessert recipes have all been ""en-lightened"" with fresh produce, low-fat dairy products and flavorful multiethnic ingredients. Calorie-laden Chicken Divan, for example, has given way to Marinated Grilled Chicken with Mango Salsa; grape jelly and chili-sauced cocktail meatballs cede their space to piquant Pickled Shrimp. Toasted Mushroom Rolls made with crustless slices of white bread rolled thin are minimally modified (calling for exotic mushrooms if available). Where once there were instant mashed-potato flakes, canned vegetables and Jello, there is now Polenta with Wild Mushrooms, Parmesan Braised Fennel and fresh Strawberry Sorbet. Two souffles, which can be prepared in advance and baked at the last minute, are standouts. Burros provides useful tips (e.g., how to pasteurize egg yolks), offers several knockout short-cut pie crusts, lists mail-order sources and includes a chapter with 10 menus plus ""game plans."" Above all, this collection once again encourages home cooks to be guests at their own parties. (Apr.)